People who use caulk face two challenges, getting a new tube started and getting a partially used tube started.
To start a new tube, the user uses a razor knife to cut the tip off the nozzle and then a long nail or coat hanger to puncture the seal at the base of the nozzle. It is far from uncommon for the hole in the tip to end up oversize due to the need to accommodate the nail. The result is an oversize bead.
Starting a partially used tube presents its own set of frustrations. Many a nearly full tube of caulk has become unusable because the caulking material in the nozzle has hardened. While a session with a coat hanger or the like can sometimes re-establish the pathway between the usable caulk in the tube and the tip of the nozzle, such measures tend to be ineffective, and the result is likely to be a series of spurting globs rather than a smooth bead.
A more elegant alternative to the coat hanger approach is disclosed in U.S. Pat. No. 4,284,213. The patent discloses a screw-on caulking nozzle engagable with a threaded nipple on the tube, and a cap having external threads also engagable with the threaded nipple. To start a new tube, one can unscrew the nozzle and break the seal. In the event that the nozzle becomes clogged, it is a simple matter to unscrew it and remove the hardened material with a screwdriver, coat hanger, or other tool of choice.
However, a quick visit to the hardware store will reveal that the vast majority of tubes of caulking material do not have the threaded connection, but rather have a non-removable nozzle.